1. Field of the Invention
The invention described herein relates to trajectory planning and execution for movable components of a photolithography system.
2. Related Art
Many industrial processes involve motion along trajectories that are defined by precise positions at specific times. Photolithography is an example of such a process. In a photolithography process, an illumination source projects an illumination beam. The beam passes through, or is reflected off of, a reticle to enable the transfer of a reticle image from the reticle to a substrate, such as a semiconductor wafer.
Scanning techniques are employed in photolithography processes to project a reticle image into a substrate. These scanning techniques involve moving a reticle across an illumination slot to allow the reticle image to be exposed onto a substrate that is simultaneously moving. Reticles and substrates are exposed on stages that are capable of motion in one or more dimensions.
In general, digitally-calculated motion trajectories enable high-precision multi-axis motion control systems to achieve high throughput. Of special interest are the motion trajectories followed by the wafer and reticle in a step and scan lithography tool during the process in which the reticle pattern is imaged and exposed onto the wafer surface. The entire wafer surface is exposed in a sequence of field scans. The exposure of each field requires that the wafer and reticle be simultaneously scanned across the exposing field of the imaging optics at precisely synchronized, constant velocities. The ratio of the reticle and wafer velocities must exactly match the magnification of the imaging optics.
To maximize system throughput, it is desirable to expose a wafer in the minimum possible time. In a typical trajectory used to expose a wafer, after each field exposure, the wafer stage must be asynchronously stepped from an initial state (i.e., a position and velocity) at the end of a field scan, to a new state (i.e., a new position and velocity) at the start of the next field scan. Similarly, the reticle stage must also be asynchronously stepped from an initial state at the end of a field scan, to a new state at the start of the next field scan. Consequently, minimizing the amount of time between scans would improve system throughput. A system and method is therefore needed to plan and execute optimal trajectories for photolithography components for the intervals between constant velocity scans.